Solvent treating of mineral oils



F a. H. B. DAVIS SOLVENT TREATING OF MINERAL OILS Filed April 6, 1938 DIS 772 LA TE x v m j a r a i M W 7% N T u vc G J m m 5 r E m R T Patented Aug. 19, 1941 SOLVENT TREATING or MINERAL oILs I Garland H. B. Davis, Elizabeth, N. J., assignor to Standard Oil Development Company, a corpora tion of Delaware Application April 6, 1938, Serial Not 200,326

3 Claims. 01. 196-13) The presenttinvention relates to an improved method of solvent treating mineral oils. It particularly relatesto a method of treating hydrocarbon fractions by treating continuouslyconstituents of said fraction of progressively higher boiling points. The invention especially relates to a process of distilling a petroleum fraction,

taking overhead constituents of said fraction having progressively higher boiling points and treating said constituents continuously by means of a selective solvent.

It is well known in the art to separate mineral oil as, for example, petroleum hydrocarbons, into a relatively more aromatic andinto a relatively more parai'linic fraction by means of selective solvents as, iorexample, phenol, furfur'al, liquid sulfur dioxide, etc., and also by means of liquefied norm-ally gaseous hydrocarbons and the like. In these. processes a relatively wide boiling range fraction is treated with one or more solvents having the ability to segregate the fraction into relatively more aromatic and into relatively more paraflinic fractions.

,, Particularly in the manufacture of lubricating oils having high viscosity indexes, it is very desirable that therelatively more. aromatic constituents be removed. In usual processes the practice is to distill or top crudes in order to secure the lubricating oil distillate and then to distill the lubricating oil distillates under non-cracking conditions to -secure the desired lubricating oil fraction. The lubricatingoil distillate or the redistilled distillate may be treated with sulfuric acid followed by a caustic soda neutralization treatment. Waxy distillates may alsoybe dewaxed by any desirable procedure as, for example, by chilling and pressing or by means of solvents. These lubricating oil fractions prepared by various com binations of the above described steps are then further treated with various selective solvents to remove the relatively more aromatic type compounds in order to secure a high quality lubricating oil. The usual method of treating is to subject the entire fraction to the effect of a selective "solvent or to the eiiect of various mixtures of selective, solvents.

" This process, howevenhas the disadvantage that the selective solventswhich will dissolve the relatively more aromatic compounds also have the tendency to preferentially dissolve lower molecular weight fractions. Thus it may be readily seen that the efiiciency of separation of the more aromatic from the more paraflinic compounds is lessened depending upon the extentto which the particular boiling point fraction being treated differs in boiling range and molecular weight. My improvedprocess is a method by which a lubricating oil fraction may be solvent treated with a solvent which contacts aromatic and paraiiinic compounds of approximately the same molecular weight, thereby greatly increasing the efficiency of the solvent extraction treatment and also securing an improved lubricating oil product.

The process of my invention treats a mineral oil fraction by treating constituents thereof of progressively higher boiling point in a continuous manner and thus treats infinitesimal fractions of approximately the same molecular weight, thereby attaining the maximum optimum efficiency in regard to the separation of the more aromatic from the more paraflinic constituents.

The process of my invention may be readily understood by reference to the attached drawing illustrating one method of carrying out the same. In the drawing I represents a tower or similar equipment which may be heated and gradually raised in temperature by any suitable means. The desired lubricating oil fraction is introduced into this tower by means of feed line 2, controlled by valve 3. When the desired quantity is in the tower or similar equipment, the temperature is gradually raised in tower I and constituents of progressively higher boiling point of said fraction are taken overhead through line 4 and passed through cooler 5 into distillate drum 8. Non-condens'able gases are removed through line I. The condensed overhead from tower I is removed from distillate drum 6 by means of line 8 and introduced into the solvent treating system 9, in which system it flows upwardly through tower 9 intimately contacting adown flowing solvent introduced into treating system 9 by means of feed line I II. The raifinate of tower 9 is removed by means of take-off line II and the solvent extract of treating system 9 by means of take-01f line I2. In this system the overhead from tower I is continuously treated by means of a solvent in treating system 9. Any residue which is not distilled in tower I when the maximum temperature desired is reached is removed through take-off line I3.

Tower I may be of any suitable construction and is preferably a batch vacuum still. This tower may be equipped with suitable insulating, heating and cooling means and may contain distributing and fractionating trays and the like. The towerymay also be equipped in any desired manner to secure desired optimum temperatures and pressure conditions and may also be equippedto distill any particular charged stock by means of fire and steam.

The solvent treating equipment may be of any desirable design as, for example, a countercurrent treating tower or may be a seven-stage batch treater. If a solvent treating tower is employed, the tower is preferably of a small diameter and may contain suitable distributing and contacting means. The tower or stage treater may be equipped to feed in the overhead from the still at any desired point.

Suitable selective solvents may be any of the well known class of solvents which have preferential selectivity for aromatic type compounds as, for example, phenol, furfural, ch lorex, liquid sulfur dioxide, ethylene diacetate, tri-cresyl phosphate and the like as well as dichlorethyl ether, nitrobenzene and the like.

The method of operating according to the present invention is to charge the still with the desired charged stock and then to gradually raise the temperature. as in a vacuum batch still operation. The overhead from the still is then led continuously through the solvent treater wherein it intimately contacts the particular solvent selected. The quantity of solvent used at any stage of the process is a function of the quantity of material taken overhead at this stage. For example,it maybe desirable to have a solvent ratio of one volume of solvent per one volume of overhead at the initial stages of the operation and to increase the solvent ratio to six or ten volumes of solvent per volume of overhead in the later stages of the operation. It may also be desirable to change the actual solvent being used in the initial stages from that being used in the later stages of the continuous operation.

The following table, for example, demonstrates how the volume of solvent used per volume of overhead may be varied as the overhead is continuously being treated:

Table I Volume of solvent per volume of overhead Percent overhead as temperature gradually rises V Solvents of de- Percent overhead as temperature gradually rises creasingtselec- Sulfur dioxide. Furfural. Aniline. Phenol.

Depending upon .the particular material being treated and the results desired, itmay be desirable-to select solvents in.the order opposite to that, shown in the'above table.

Although my invention may be applied to the treatment of any mineral oil, it is particularly desirable in the preparation of improved lubricating oils. The process as applied in the preparation of a lubricating oil is shown by the following example.

Example A lubricating oil fraction boiling in the range from about 600 to 850 F. at atmospheric pressure is introduced into a vacuum batch still I. The temperature in this still is gradually raised and the lubricating oil is taken overhead under noncracking conditions and passed through cooler 5 into the distillate drum 6. The condensed overhead from tower l is introduced at the bottom of solvent treating system 9 in which it flows upwardly through tower 9 intimately contacting downfiowing phenol. The ratio of phenol to lubricating oil is about one volume of phenol per one volume of lubricating oil. The ratio of phenol is gradually raised so that when 25% of the oil has passed through the treater, the ratio of phenol to oil is approximately two volumes of phenol per volume of oil. In a similar manner the ratio of phenol to oil is gradually raised so that when 50% of the oil has passed through the treater, the ratio of oil to phenol is approximately 3:1 and when 75% of the phenol has passed through the treater, the ratio of phenol to oil is approximately 4:1. When the last portions of the overhead are taken through the treater, the ratio of phenol to oil is approximately 5:1.

The above example is given for purposes of illustration only and is not to be construed as limiting the invention in any manner whatsoever. The ratio of solvent to oil being treated may be maintained at a constant ratio or may be varied widely to secure optimum results. Any particular solvent may be used or a combination of solvents may be used. The selectivity of the solvents may be adjusted in any manner desirable as, for example, by the addition of water or any other suitable material.

The process of the present invention gives particularly desirable results when treating mineral oil fractions containing constituents, the boiling points of which change rapidly with molecular weights. Thus the process of the present invention is particularly desirable for the solvent extraction of relatively low boiling petroleum oil distillates as, for example, those distillates boiling below 700 F. at atmospheric pressure. The process gives especially improved results when treating petroleum oil distillates boiling in the naphtha and kerosene range. It is to be understood that the process may be widely modified. For example, reflux may be pumped back into tower l or the tower may con-, tain a partial overhead condenser or any other suitable means of securing reflux may be employed.

Treating system 9 may also be modified as, for example, the solvent extraction operation may be carried out in a manner in which reflux is employed.

It is also within the scope of this invention to treat the constituents of progressively higher boiling points taken overhead in the vapor phase with :a solvent. In this manner of operating the solvent would contact the vapors before condensation of the vapors occured. It may be de-. sirable in this type of operation to utilize a par-. tial overhead condenser, returning the condensat as reflux t tower l. emovin h a s and contacting the same with the solvent prior to condensation of the vapors. The partial condenser could, however, be placed anywhere in the system and the condensed portions of the overhead returned to the tower by means of a pump.

The invention is not to be limited by any theory or mode of operation, but only by the following claims in which it is desired to claim all novelty insofar as the prior art permits.

I claim:

1. Process for the solvent treatment of petroleum oil fractions boiling in the range from about 600 F. to 850 F. at atmospheric pressure and containing aromatic and parafiinic type constituents of relatively high and relatively low boiling points comprising batch distilling said petroleum oil fraction under vacuum conditions in a manner to remove overhead progressively higher boiling point aromatic type constituents and paraffinic type constituents having substantially the same boiling points, continuously treating said overhead fractions with a phenol in a manner that the initial overhead fraction comprising the relatively lower boiling point aromatic and paraffinic constituents is contacted with about 1 volume of phenol per 1 volume of overhead oil, grad ually raising the quantity of phenol so that when about 25% of the oilhas passed overhead the ratio of phenol to oil is approximately 2 volumes of phenol per volume of oil, that when 50% of the oil has passed overhead the ratio of phenol to oil is approximately 3 to 1 and that when of the oil has been taken overhead the ratio of phenol to oil is approximately 4. to 1.

2. Process for the solvent treatment of a petroleum oil containing aromatic and paraffinic type constituents of relatively high and relatively low boiling points comprising batch distilling said petroleum oil in a manner to remove overhead progressvely higher boiling point aromatic type constituents and paraffinic type oil constituents having substantially the same boiling point, continuously treating the progressively higher boiling point overhead oil constituents with a solvent selected from the class of substances characterized by having a preferential selectivity for the relatively more aromatic type constituents as compared to the relatively more paraffinic type constituents in a manner that the ratio of solvent to overhead oil constituents is substantially progressively increased as progressively higher boiling point constituents are treated, under conditions to continuously form a raffinate phase and a solvent extract phase, continuously separating the respective phases and removing the solvent therefrom.

3. Process in accordance with claim 2 in which the ratio of solvent to oil is at least doubled during the batch distillation operation.

GARLAND H. B. DAVIS. 

